Sensory irritation of the upper respiratory tract is being measured in animals exposed to various airborne chemicals to define how sensitization or desensitization may occur under various exposure conditions particularly with repeated exposures such as in industrial situations. An attempt is made to relate exposure concentration with the degree of response obtained and to define an analytical technique relating various concentration rise time to the degree of response observed. The animal model is being tested with mixtures of sensory irritants for useful predictions for human exposures. Also mixtures of airborne chemicals which have no sensory irritating properties but when irradiated (u.v.) may yield potent sensory irritants, such as in photochemical smog, will be tested in an attempt to define the conditions under which humans are likely to experience sensory irritation. Two components of photochemical oxidants, acrolein and formaldehyde, are investigated to determine the total reaction to each and to their mixtures.